Known force measuring devices using diaphragms comprise a circular base plate to the peripheral rim thereof an elastic diaphragm is bending elastically fixed, the diaphragm being provided with a force introduction projection at its top surface at a central position. For force measurement, strain gauges are provided on the surface of the diaphragm at locations undergoing strongest bending. The fixing of the strain gauges to the surface of the diaphragm is complicated; furthermore, the strain gauges are sensitive to environmental influence and the signal generated is relatively weak.
In the German Patent Publication No. 1,129,317 a force measuring device is disclosed which uses a displacement sensor inductively operating for sensing a displacement of a diaphragm by means of a feeler. The diaphragm is fixed around its periphery to a rigid ring attached to the base plate. The diaphragm has a quite specifically varying thickness in radial direction. Thus, it is difficult to manufacture. Apparently, the inductive sensor shown needs a relatively large displacement of the diaphragm in order to generate a reliable signal. Therefore, specific measures are necessary to compensate a change in gas pressure within cavity formed between the diaphragm, the ring and the base plate. Since the base plate is fixed to the ring by screws there is no elasticity in this connection. Consequently, the device is rather sensitive against lateral forces.
U.S. Pat. No. 4,340,877 discloses a pressure transducer for providing an electrical signal representative of a pressure applied to the interior of an aneroid capsule, at least one wall thereof comprising a diaphragm. In the centre of the diaphragm a magnet is mounted opposite to a Hall-IC. A changing pressure changes the distance between the magnet and the Hall-IC in direction of a central axis of the transducer. With the known pressure transducer a separate supporting structure is necessary for mounting the Hall-IC and its associated circuits outside the cavity forming the aneroid capsule. To protect the Hall-IC and its associated circuits the whole arrangement is further enclosed in a housing. There is no possibility to use this pressure transducer for measuring forces acting upon the transducer.
The German Laid Open Publication No. 32 38 951 discloses a force measuring device using two diaphragms provided with strain gauges. The two diaphragms are connected in series by being fixed to a central bolt in parallel spaced relationship to each other. Furthermore, the two diaphragms are clapmed around their peripheries. The movement of the central bolt upon force application thereonto in the direction of a central axis is limited by an abutment provided on the interior bottom side of a potlike housing.